Figure 1.

Functionally important regions of the 70S ribosome complex (panel a). The small 30S subunit shown in transparent blue (panel a and b) contains the mRNA binding region, as well as its entrance and exit channels, together with the decoding center residues A1492 and A1493 residing on helix 44, at the interface of two subunits. The tRNA binding sites A-, P- and E- are indicated (panel a).The large 50S subunit in gray (panel a) has two prominent mobile stalks L1 and L7/L12, involved in controlling the tRNA exit and tRNA entrance, respectively. Extended ribosomal protein L9 of 50S is removed in some simulations to prevent its large dominant motions in normal mode analysis. The 30S subunit head has been reported to rotate during subunit association,¹⁰ tRNA selection⁹ and translocation,⁵ and this same type of rotation was also found in empty 70S E. coli ribosome crystal structure.¹¹ The ribosomal proteins studied and the3’ end of 16S rRNA of the small subunit are shown in cartoon representation (panel b). All molecular graphics were prepared using PyMol.⁸⁹